Documents are commonly used to present information to a reader. For example, spreadsheets may be used to organize data into a visually attractive and consolidated format. The contents of a document such as a spreadsheet are often assumed to be valid and accurate. However, errors may occur when text or data, such as numeric or text data, is entered into a document, such as when a new document is derived by copying data blocks from an existing document. Errors may be entered due to typographical errors, phonetic errors, mathematical errors, or other sources of error. In other cases, errors may be generated during transmittal of a document via a network or other connection. These and other sources of errors in document data may cause problems for systems or persons relying on the accuracy of such text or data.